1. Field of the Invention
This invention relates to novel compositions of doped fluorophosphates glass. The new and improved glass compositions are particularly useful in laser glass, amplifiers and high density optical storage applications and are based on or contain Ba(PO3)2, AL(PO3)3, BaF2 or related fluorides and MnO; or oxides or fluorides of rare earth elements: Nd, Er, Tm, Ho, Pr, Tb, Yb, Sm and Eu; and mixtures thereof.
2. Description of Related Art
Presently most optical laser glasses are manufactured on a SiO2 base. The SiO2 based laser glasses have a limited refractive index of nD=1.40 to 1.45 and a limited infrared transmission spectrum. These limitations prohibit use of SiO2 based glasses in applications for modern laser applications such as the need for glass with efficient transparency in the near and mid infrared frequency range.
There are disclosures of fluorophosphates glass compositions in existing art; however, none of the existing glass compositions provide the efficient transmission qualities of the present invention in the near and mid infrared frequency range used in modern laser applications. Fluorophosphate laser glasses have a higher refractive index and dispersion than glasses with silicon dioxide. The fluorophosphates glasses generally have a refractive index of nD=1.6344 to 1.6412. They can be used as the basis for creating high power lasers.
Fluorophosphate glasses are close to the phosphate glasses in terms of the degree of covalence of the dopant-ligand bond. This has been confirmed by comparison of the Racha coefficient, B, for these glasses. The magnitude of B decreases with a decrease in size of the effective nuclear charge of free ions. The boundaries of glass formation for fluorophosphate glasses with metaphosphates of barium and aluminum and with fluorides of alkaline earth elements create a wide domain of glass forming fluorophosphates that increase in the following order Ba>Sr>Ca>Mg. The presence of barium fluoride, BaF2, with RFx where RFx is from the group MgF2, CaF2, PbF2 and BiF3 effectively increases chemical durability of laser materials.
The phosphate laser glasses of varying composition due to thermal expansion and hardness properties and to low chemical durability or stability are not suited for the laser applications anticipated for the instant invention. These limitations are generally due to the presence of metaphosphates of lithium, sodium and potassium, U.S. Pat. No. 3,846,142.
Existing fluorophosphates laser glass such as the system BaPO3F—MgF2—Nd2O3—Ga2O3—MnO have a high rate of inactive absorption of wavelength 1,064 nm, which reduces the luminescence of glass dopants. There also exist a class of fluorophosphate laser glasses that were developed on a base of metaphosphate aluminum and fluorides of metal from the first and second group of the periodic elements. The optical constant for these glasses are in the range (nD) from 1.45 to 1.59 whereas the instant invention exceeds 1.60 for greater laser efficiency, U.S. Pat. Nos. 2,511,225; 2,511,227; 2,481,700 and 2,430,539.
There are several publications that discuss compositions of fluorophosphates glass; however, they do not disclose or anticipate the specific composition of the present invention. Example text references are: Journal De Physique V 4n4, April 1994, Pages 509-512, article of R. Balda, J. Fernandez and A. DePablos.; Journal of Non-Crystalline Solids, Vol. 213-214, June 1997, pages 245-250, article of J. L. Adam, N. Henry Duhamel and J. Y. Allain; and Journal of Chinese Physics Lasers, Chin. Phys. Lasers, Vol. 16, No. 4, April 1989, pages 227-232.